Electronic
Projection System Terms

Active
MatrixEach
pixel is actively controlled by a diode or a transistor. Advantage: allows
each pixel to be independently controlled.

ANSI
LumensANSI
lumens is a scale to measure the overall brightness value for projectors.
The measurement represents the average value of 9 points on the projected
screen image.

Aspect
RatioThe ratio
between the width and height of the output (whether it is a monitor, LCD
projection panel, overhead or slide).

ANSIAmerican
National Standards Institute.

CGAColor
Graphics Adapter. This is the card added to an IBM® PC & XT that
gives the computer the ability to handle graphics and color. Resolution
of this card is 640 x 200 pixels.

Composite
VideoA video
signal that combines all the color and timing components of the image into
a single input line.

Compression
ModeA method
of displaying images in a reduced size format. A compressed image usually
has part of the image information discarded. The result is a projected
image that has light and dark lines and text characters with thick and
thin line widths.

Contrast
RatioThe ratio
of the brightest and darkest images a display can reproduce.

Convergence The alignment
of the red, green, and blue video image signal on a projected display system.

Display
SizeDisplay
size is the diagonal length of the LCD plate. Typical sizes are 8.4" to
12.1".

DSTNDouble
Super Twist Nematic. Where two separate LCD plates are combined to form
a single panel.

Distribution
Amplifier A device
that amplifies and transmits a video signal over a distance using shielded
coaxial cable.

EGAEnhanced
Graphics Array. This card is the second generation of the CGA card in that
it gives IBM PCs, XTs and ATs greater resolution (640 x 350 in all models).

Hz,
(KHz, MHz)Hertz
or (Kilohertz or Megahertz). Cycles per second. (Kilo = 1,000, Mega = 1
million). These terms are used to express the frequency of an electrical
signal or event.

Non-InterlacedEach
line is scanned during each total vertical (full) screen refresh.

NTSCNational
Television Standards Committee. The standard for broadcast color television
and other video equipment signal in North America, established in 1953.
525 lines/60 Hz.

PALPhase
Alternate Line. The phase of the color carrier alternates from line to
line. PAL is used extensively in Western Europe. 625 lines/50Hz.

PaletteThe number
of colors available for use in creating an image. The use of a standardized
palette in a presentation allows the user to create a consistent look.

PanelThe same
as liquid crystal display (LCD).

Passive
Matrix The use
of simple driver electronics in an LCD projection panel where the pixels
are turned on and off using a row-and-column format. The amount of control
on each pixel is limited, which results in lower contrast ratios and a
slower response time than active-matrix LCD projection panels.

PixelA unique
position on a display that consists of a single dot or group of three dots
(red, green and blue). Total pixels are usually expressed in horizontal
x vertical dimensions (e.g., 640 x 480).

Polysilicon
TFT Polysilicon
TFT is a type of LCD technology that allows more light at high temperatures
through the LCD.

Refresh
RateThe number
of times the screen image is "painted" or refreshed per second, expressed
in Hz.

ResolutionResolution
is the ability of an imaging system to faithfully reproduce fine detail
information and transitions between dark and light parts of an image. The
more pixels the display systems can address (e.g., 800 x 600 ) the higher-quality
image with more detail.

Response
Time The time
it takes for a pixel to turn on and off. Typically measured in milliseconds,
an active-matrix LCD projection panel's response time is fast enough to
display full-motion video and rapid mouse cursor movements.

TFTThin
Film Transistor. This is a developing technology that attempts to place
the controller of the panel directly on the surface of the glass.

TransmitivityThe percent
of the light that is transmitted off the stage of the overhead projector
that reaches the screen at a given distance. Typically, LCD projection
panels are able to use less than 10% of the total light available.

TSTNTriple
Super Twist Nematic. Where three separate LCD plates are combined to form
a single panel.

VESA
StandardA set
of display specifications agreed upon by the VESA organization, usually
referred to by resolution and vertical refresh rate.

VGAVideo
Graphics Array. This is the standard interface for the IBM PS/2®. It
is the only analog graphics card IBM has used (other cards handle digital
information) 720 x 400 in the text mode, graphics mode 640 x 480 resolution.

VideoThe capability
to project images from a VCR, laser disc, or PC with CD-ROM drive.

VirtualMouse
Remote Control3M's
lightweight remote control offers all of the functionality of a computer-compatible
mouse.

Y-CableWith
many computers, there is only one monitor output. Subsequently, a cable
is necessary that will split the monitor signal so it will work simultaneously
with both a monitor and an LCD projection panel.

Overhead
Projector Terms

AC
OutletsUnswitched
AC power outlets for connecting accessory items such as notebook computers.

ApertureThe area
of the stage that is available for projecting an image. Usually comes in
the following sizes: 10" X 10", 10.5" X 10.5" and 11.25" X 11.25" (A4).

Articulated
HeadA closed
projector head, where the mirror will move one-half the distance when the
image is tilted up on the screen.

Coated
StageHard
coating on a reflective optical stage (Fresnel lens) that resists scratching,
so that the projected visuals stay sharp and clear.

Color
TuningAdjusts
the edge-to-edge uniformity of the projected light to eliminate yellow
or blue corners. This gives an optimized image, no matter what the projector-to-screen
distance, within the prescribed area.

Closed
HeadA projection
head where the mirror and lens is enclosed.

Convection
CooledCooling
of the projector lamp by the upward flow of heated air, without the use
of a fan. Usually used in reflective-type projectors that have the lamp
installed into the head assembly.

Doublet
LensA projection
lens that has two elements contained in a single assembly.

Elevation
AngleThe elevation
that the projected image can be tilted to, and still project a full image
onto the screen.

Focal
LengthThe value
given to a lens, stated in inches or millimeters. The smaller the focal
length, the wider the angle of the image. Focal length is the distance
between the lens and its focal point.

Focus
CorrectionA feature
that is used when it is necessary to project an image onto a vertical surface
(such as a wall) with a high tilt angle of the head, making it possible
to obtain uniform focus from top to bottom of the image. This feature does
not eliminate keystoning.

Fresnel
LensA flat
lens that is composed of a series of closely spaced grooves that control
the refraction of light. It is usually part of the stage.

High/Low
Intensity SwitchA control
switch that decreases (LOW) the lamp output by 10% and doubles the lamp
life. The HIGH setting should be used with LCD projection panels.

IlluminationThe density
of light projected onto a screen or other surface. Stated in lumens.

KeystoningKeystoning
is caused when the projected image is not perpendicular to the screen.
Correct keystoning by tilting the screen until it is perpendicular to the
light beam axis.

Lamp
ChangerA control
mechanism that allows easy exchange of replacement lamps by rotating a
replacement lamp into operation position after the primary lamp has failed.

Let
Run ThermostatSee Post
Cool Thermostat.

Liquid
Crystal Display (LCD)A display
panel that sits on top of the projector stage, which creates an image that
is generated by a computer.

LumenThe unit
of illumination on a screen or other surface. One lumen is the light of
one candle power on each square foot of a surface of a sphere at a radius
of one foot from the light source.

Open
HeadA projection
head where the mirror and lens is not enclosed. The image is raised on
the screen by tilting the mirror up.

Optical
TuningSee Color
Tuning.

Overheat
ThermostatTurns
the lamp off if the projector reaches an unsafe temperature.

Post
Cool ThermostatA thermostat
that allows the projector fan to continue to run after the lamp has been
turned off, which reduces the temperature of the unit.

Reflective-Type
ProjectorAn overhead
projector where the light source is located in the head assembly and shines
down onto the stage. The light is then reflected from the Fresnel lens,
back through the head and onto the screen. Usually used in lightweight,
portable projectors.

Safety
ThermostatSee Overheat
Thermostat.

Singlet
LensA projection
lens that has only one element.

StageThe flat
area of the projector where the transparency film or LCD projection panel
is placed.

Transmissive-Type
ProjectorAn overhead
projector where the light source is under the stage and light is transmitted
through the transparency film to the head and onto the screen.

Triplet
LensA projection
lens that has three elements contained in a single assembly.